Mass spectrometry using a plasma ion source, for example, ICP mass spectrometry is useful in analyzing inorganic elements, especially a trace amount of metal, and is widely used in many fields including semiconductor, geological and environmental industries. ICP mass spectrometry enables substantial and simultaneous multi-element analysis on most elements in the periodic table, and the concentration of an element can be quantitated with an excellent level of sensitivity in the order of one billionth (ppb) or one trillionth (ppt).
An ICP mass spectrometry apparatus uses inductively-coupled argon plasma as an ionization source; and ions of analyte elements generated by the plasma are introduced as a beam into a mass spectrometer; and separated and measured depending on the mass-to-charge ratio (m/z). That is, analyte elements are dissolved in a sample solution and sent to a nebulizer to generate a sample aerosol by a pump together with elements added as an internal standard. The sample aerosol is supplied to plasma, and, then, desolvated, atomized and ionized. The resultantly obtained element ions are conveyed from the plasma to the mass spectrometer through an interface and an ion lens having two orifices known as a sampling cone and a skimmer cone. However, in many cases, in order to eliminate the influence of interference ions, a collision/reaction cell is arranged subsequent to the ion lens. The collision/reaction cell introduces thereinto a reactive gas with a relatively small molecular weight such as hydrogen or an inert gas such as helium to selectively neutralize polyatomic molecule ions in the introduced ion beam by reaction with gas molecules or to cause the loss of kinetic energy by collision, thereby preventing the interference to measured signals.
In the meantime, for conducting actual measurement by use of an ICP mass spectrometry apparatus, it is necessary to set the time for sample uptake/rinse, selection of internal standard elements to be used, a plasma condition, a gas condition for a collision/reaction cell, and an integration time in a mass spectrometer and to create/determine an analytical method suitable for the sample. Of conventional measurement method creations for ICP mass spectrometry apparatus, there is a method wherein a user selects from preset methods created for preliminarily expected conditions. This method is convenient for a sample, from which an object to be measured is easily expected, like measurement pertaining to laws and regulations, such as the quality of tap water, but it is necessary for a user to optimize conditions in the case of a sample outside the conditions of the preset methods. Further, in the case of: a sample for which it is difficult to select a plasma condition or a gas flow rate due to the influence of co-existing matrix; an unknown sample to which whether existing methods are applicable or not is unclear; and a sample, for each lot of which a different method is preferably used, a measurement method with an appropriate condition is conventionally determined by a user based on a plurality of measurement results. However, this may be largely dependent on experience and intuition of a user and is a complicated work that requires time and effort.
Patent Document 1 (Japanese Patent No. 4,903,515) discloses a technique for automatically determining by a computer program conditions such as the flow rate of carrier gas in an aerosol and the RF output of plasma using the relationship in sensitivity between a specific metal ion and oxide ions of the metal ion. This is suitable for optimizing a plasma condition in response to, especially a high matrix sample, but is unable to automatically create a mass spectrometry method over the entirety of an ICP mass spectrometry apparatus. Further, Patent Document 2 (Japanese Patent No. 4,822,346) discloses a system for diagnosing and correcting apparatus characteristics of an ICP mass spectrometry apparatus. However, this also mainly relates to the calibration of parameters pertaining to plasma, and is not able to automatically create a mass spectrometry method over the entirety of an ICP mass spectrometry apparatus.
Non-patent Document 1 (E. F. Hewitt, P. Lukulay, and S. Galushoko, “Implementation of a rapid and automated high performance liquid chromatography method development strategy for pharmaceutical drug candidates,” J, Chromatgr, A, 1107, 79-87, 2006) describes automatically creating a measurement method suitable for an analyte sample by a computer though it relates to liquid chromatography. However, this method conducts modeling of a retention time of chromatography and creates a measurement method in an off-line mode. Thus, it cannot be used for an ICP mass spectrometry apparatus of a different measuring method.